This application corresponds to Japanese Patent Application No. 8-318356, filed on Nov. 28, 1996, which is hereby incorporated by reference in its entirety herein.
1. Field of the Invention
The present invention relates to a variable resistor and, more particularly, to a residue-proof (e.g., dust-proof) variable resistor equipped with a case. The invention also pertains to a method for producing such a variable resistor.
2. Description of the Related Art
FIG. 36 shows a conventional variable resistor. The variable resistor 180 comprises an alumina substrate 184 having on its surface a horseshoe resistor 181, collector electrode thin film 183 and electrode thin films 182 respectively connected to end portions of the horseshoe resistor 181. A case 185 is provided for accommodating the alumina substrate 184 therein. Three lead terminals 186 (one of which is shown in FIG. 36) are allowed to pass through the alumina substrate 184 and are respectively soldered to the electrode thin films 182 and 183. A rotor 187 is accommodated in the case 185. A slider 189 is disposed on a rear surface of the rotor 187. A sealing O-ring 190 is disposed on the rotor 187 and a resin 191 is provided for sealing an opening in the rear surface of the case 185. Furthermore, when this variable resistor 180 is configured into a so-called "side surface adjusting type variable resistor", wherein the resistance value is adjusted by rotating the rotor 187 from an arrow-indicated direction illustrated in FIG. 36, the lead terminals 186 are bent along the rear surface of the case 185.
An explanation will be given of the terminal numbers 1, 2 and 3 illustrated in FIG. 37 with reference to FIG. 38. It is now assumed that the lead terminal number 2 is the terminal connected to the slider 189 brought into sliding contact with the resistor 181. Next, it is assumed that the lead terminal number 3 is the terminal electrically connected to the end portion side of the resistor 181 on a side such that when the rotor 187 is rotated to the right the resistance value between this lead terminal and the lead terminal corresponding to the terminal number 2 becomes smaller. Finally, the lead terminal number 1 is the terminal electrically connected to the other end portion side of the resistor 181 on a side such that when the rotor 187 is rotated to the right the resistance value between this lead terminal and the lead terminal corresponding to the terminal number 2 becomes larger.
In the variable resistor 180 of the side surface adjusting types various combinations are made among the resistance value adjusting direction, lead terminal pitches and lead terminal numbers. To accommodate these changes, it was necessary that many kinds of constituent parts be prepared and many kinds of processing methods be executed. In particular, regarding the complex bending of the lead terminals 186, as illustrated in FIG. 37, two kinds of initial bending are included (i.e., a case where the lead terminal is bent into the lead terminal 186 indicated in a solid line shown in FIG. 36 and a case where the lead terminal is bent into the lead terminal 186' indicated in a one-dot chain line shown in the same figure). There are three kinds of subsequent bending, including a first kind corresponding to a state in which the terminal numbers 1, 2 and 3 are arranged in one row in this order, a second kind corresponding to a state in which the terminal number 2 is located on the left side of the terminal numbers 1 and 3, and a third kind corresponding to a state in which the terminal number 2 is located on the right side of the terminal numbers 1 and 3. This is shown in FIG. 37. The second column of permutations in this figure corresponds to the initial bending operation and the third column of permutations in this figure corresponds to the subsequent bending operations. More specifically, the third column represents a view of the components taken from the direction As after completion of all bending steps.
The subsequent bending after the initial bending is three in kind with respect to each of the two kinds of initial bending. Thus, six bending methods become necessary. This made the manufacture and management of these parts complex, which hindered productivity.